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Topic: S35 Fuel bladder (Read 970 times)

We recently replaced the starboard fuel bladder on our S35. The new bladder has been in for 8 weeks and started to leak. The AP found a hole below the filler inlet, they claim it has been punctures by improper nozzle use when filling. We noted the bladder would balloon up when low on fuel and the hole is close to the area of the fill tab corner.

I am a partner of Robert James on the S35 that he writes about (disregard the tail number differences, as this is stale info, our current tail number is N327D). Here are some images of the damage that he is talking about.Mikhail Belov2010-09-21 00:57:17

That looks more like the cell lifting and constantly rubbing on the corner of the tab than from a fuel nozzle. First thing I would do is to put a good radius on the two corners of the tab before it's reinstalled.

Now, to lift that much and cause that kind of damage, at least to me, it would appear you have a vent issue that's causing the cell to collapse from the bottom up since only fuel and the weight of the material holds it down. It is normal if the tank sits empty for more than a couple of weeks for it to lift some, but that will go back to normal once fuel it added back.

You need to investigate the entire vent system, especially the vent drains at the root of the rear of the underside of the wing. If they are not positioned properly, ie. they are bent back, they can cause a severe vacumm in the tank causing it to lift. You would also see fuel loss if this is happening. Conversly, if the vents are positioned too far forward, it can pressurize the tank much more than it's designed to be.

And it's odd that there is no additional rubber pad on the inside of the cell. Most new cells I've seen in the past 20 years, including the ones I installed in our S model long ago, have an additional rubber pad installed directly below the fuel port opening to prevent fuel nozzle damage to the cell itself.

Interesting. I guess the edges of the pad are not visible in the photo. Ours is about 1/16" thick flexible but solid rubber with a raised rib pattern parallel with the wing that they glue in place with some really good adhesive. It's about 8" square. Ours are from Floats and Fuel Cells from about 15 years ago.